This invention relates to multilamp photoflash units and more particularly, to a photoflash unit having an array of lamps connected to a printed circuit board and positioned over the surface thereof.
U.S. Pat. Nos. 3,894,226 and 4,017,728 describe a photoflash unit, referred to as a flipflash, which comprises an elongated planar array of eight high voltage type flashlamps mounted on a printed circuit board with an array of respectively associated reflectors disposed therebetween. The flipflash circuit board comprises an insulating sheet of plastic having a pattern of conductive circuit runs, including the terminal contacts, on one surface. The flashlamp lead-in wires are electrically connected to the circuit runs by means of eyelets secured to the circuit board and crimped to the lead-in wires. The circuitry on the board includes a plurality of printed, normaly open, connect switches that chemically change from high to low resistance so as to become electrically conducting after exposure to the radiant energy from an ignited flashlamp operatively associated therewith. The purpose of the switches is to provide lamp sequencing and one-at-a-time flashing. The overall construction of the flipflash unit comprises front and back plastic housing members with interlocking means for providing a unitary structure. Sandwiched between the front and back housing members, in the order named, are the flashlamps, a unitary reflector member, preferably of aluminum-coated plastic, shaped to provide the eight individual reflector cavities of the array, an insulating sheet, a printed circuit board, and an indicia sheet, which is provided with information, trademarks and flash indicators. Each of the individual reflectors has a concave (generally parabolic) surface with the lamps being disposed within this concavity; the rear surface of the reflector has holes or slots to permit light and heat radiation to pass through for actuating the circuit board switches and flash indicators. In this manner, the heat to which the circuit board switches are exposed is controlled by the reflector openings. Further thermal protection for the circuitry is provided by a clear plastic insulator sheet which is interposed between the reflectors and the circuit board and functions both as a heat insulator and means for reducing the amount of heat which activates the heat-sensitive switches on the circuit board. With the maximum amount of reflector surface available behind the lamp, the optimum output efficiency is achieved.
In more current design concepts, the trend is toward providing a photoflash unit construction which is more compact, simplified and cost-efficient. More specifically, it is desired to eliminate the separate multicavity type reflector element. U.S. Pat. No. 3,608,451 to Kelem discloses a flash array having a reflector in the form of a metal coating on a circuit board, the circuit board being larger than the reflector coating so as to provide areas for circuit runs. The reflector coating of the Kelem flash array also functions as the common circuit conductor connected to one lead-in wire of each of the lamps. There is no switching circuitry on the Kelem circuit board.
U.S. Pat. No. 4,136,379 to Chevali discloses a flipflash array having a circuit board made of electrically insulating material having a light-reflecting surface; for example, the circuit board material may comprise polystyrene containing titanium dioxide interspersed therein. In view of the flatness of the reflector surface of the Chevali array, the front of the housing is provided with prisms to improve the distribution pattern of light when the lamps are flashed. U.S. Pat. No. 4,136,378 of Chevali discloses a flipflash array having a circuit board made of transparent electrically insulating material having a light-reflective coating on its rear surface for reflecting light when the lamps are flashed. Again, the front of the housing is provided with prisms to improve the distribution pattern of the light when the lamps are flashed. U.S. Pat. No. 4,148,093 to vanWerkhoven discloses a flash array having a circuit board in which at least a portion of the surface thereof is provided with a reflecting layer at the lamp side; light focusing elements may also be situated near the lamp.
A copending patent application Ser. No. 072,251, filed Sept. 4, 1979, and assigned to the present assignee, describes a more compact, cost-efficient photoflash unit construction comprising a linear array of electrically ignitable flashlamps mounted on a printed circuit board in the form of an elongated strip. The printed circuit board is located within the longitudinal channel of an elongated housing member having a continuous coating of conductive reflective material thereon adjacent to the lamps. A light-transmitting cover panel is attached to the front of the housing member to enclose the flashlamps. The lamps have substantially tubular envelopes and are positioned extremely close to one another with their longitudinal axes substantially parallel to the surface of the printed circuit strip and in substantially coaxial alignment. The lamps lie directly on the top surface of the circuit board onto which are screen-printed appropriate circuit runs and heat-sensitive switches. When the first lamp of the array is flashed, the heat from the lamp should close an associated heat-sensitive switch so that the seond lamp is now introduced into the circuit. However, the heat from the flashed lamp is completely exposed to the circuit and switch conductor runs. This can result in burning out the switch and destroying parts of the circuit runs, thus rendering the array inoperable. None of the aforementioned patents relating to other types of flash arrays which have eliminated the multicavity reflector member pose any solution to this problem of possible thermal damage to circuit elements.